A few times, the computer has crashed with the following symptom: the screen suddenly is filled with random, various coloured short lines and dots changing at a very rapid pace, and the machine is completely locked up--it must be reset (reset button) or powered off.

Sometimes I have the computer playing music, but most times not. Previously when the crash occurred, if there was music playing, then in addition to the screen going wild, the sound also went wild and became just a bunch of very loud rapidly changing static--kind of an aural version of what was happening on the screen, as though the CPU had run amok.

When this has happened previously, doing a reset, or a power off and then on, has restored normal operation. The machine runs cool (CPU 28-31 at idle, a few degrees above ambient, and never really reaches full load), and the case is clean.

But yesterday when this occurred, I pressed the reset button, and the screen went black (as it normally does at the beginning of a restart), but it did not restart; the monitor remained in sleep mode (black screen, power button blinking), and after about ten seconds, the computer powered off, and then five seconds later powered on, and again after ten seconds powered off and five seconds later powered on, and this continued until I held the power button for five seconds to shut it off and make it stay off. It was as though it was trying to reboot (case fans spin, CPU fan spins, hard drive and optical drive seek) without success (there was never any signal to the monitor).

I replaced the power supply with a 610W PC Power & Cooling unit, since I had it available, but received exactly the same symptoms. So that rules out the power supply, and I doubt the hard drive or optical drive could cause such symptoms.

That leaves the mainboard, the CPU, and the RAM. I just last week ran MemTest86+ for move than 5.5 hours, completing more than five complete passes, without a single error.

So, I need some input. What should I try next? I don't have either a spare CPU or a spare mainboard, so replacing either of those would mean buying a new one (expensive!), and also don't have another system to test the CPU in.

No beeps? Because there's no speaker or because your mobo/CPU is failing to beep?I wouldn't rule out RAM failure if you have no speaker connected. Memtest wouldn't have been able to test all the RAM anyway. It doesn't cost anything to use try both of your sticks alone.It also doesn't hurt to hit the mobo manual just in case there's also a LED that might be used to diagnose issues or something. But I've got to say I've seen a whole lot more bad mobos than bad CPUs. Maybe the newer ones with integrated video are more brittle though. Hopefully someone with less dated experience can chime in...

Worst case scenario, spares shoudn't be all that expensive if you buy used and aren't picky about models. Even new, there are some pretty cheap compatible CPUs. And you can resell.Or you could simply find someone local with spares...

Turn power off at the PSU switch. pull the plug after a minute. Ground yourself. Open the case and pull the battery on the mobo. Reset the CMOS. Insert the battery. Plug it it, turn it on and see if it goes to the BIOS screen.

Well, this is interesting! As noted in my first post, I had previously disconnected the power supply and connected a different power supply that I had available, but the computer had exactly the same symptoms.

Finally having a bit of time today, I put the machine on the bench, and reconnected the original power supply, getting ready to start troubleshooting. Then I plugged onto the speaker pins of the mainboard's front-panel header, a tiny beeper. To see whether there would be any beeps, I powered up the computer, and it emitted a single beep and booted normally! Tried it twice.

So, what does this indicate? Can the machine be put back into service?

My odd thought is that if it works on a bench, and doesn't work in the case, then maybe there is something causing metal-metal contact between the case and the mobo where it shouldn't be. Or, that you had a loose connector.

My odd thought is that if it works on a bench, and doesn't work in the case, then maybe there is something causing metal-metal contact between the case and the mobo where it shouldn't be. Or, that you had a loose connector.

could have also been metal debris, maybe a lost screw ect.

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Thanks for the help, guys. Sorry I didn't make myself clear: when I say I put the machine on the bench, I meant case and all, so I never took the board out of the case.

But I did redo all the connections. So it's possible there was a bad connection, or a board/case contact that changed when doing the connections, or some metal debris that dislodged when doing the connections.

So I think I'll put the machine back into service, and pray the problem does not reappear.

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